Field of the Invention
The present invention relates to a process for the remediation of the environment (for example, soil, groundwater etc.) polluted with contaminating compounds such as hydrocarbons, halogenated hydrocarbons etc. using a microorganism.
Recently, pollution of the environment such as soil and groundwater system with petroleum, aromatic hydrocarbons, or hydrocarbons such as paraffin and naphthene has been recognized. Also, the seriousness of the environmental pollution caused by organic chlorinated compounds such as trichloroethylene, tetrachloroethylene, tetrachloroethane and poly(biphenyl chloride) has been pointed out. In this situation, it is strongly desired to establish technologies to prevent the pollution from spreading and to remedy the polluted environment.
Various soil remediation processes have been proposed and carried out to restore the polluted soil to the original conditions by removing the pollutant from the soil. These soil remediation processes mainly use physical/chemical techniques such as vacuum extraction, sun-drying, aeration and oxidation. Also, processes using microorganisms capable of decomposing the contaminating compounds (bioremediation) have been studied. One of the typical bioremediation processes is so-called "indigenous microorganism stimulation method" (for example, U.S. Pat. No. 4,401,569 to Groundwater Technology Systems, Inc.) which treats a contaminated soil by enhancing the growth of the microorganisms capable of decomposing a pollutant, inhabiting the contaminated soil, and this process has already come into practical use in the remediation of petroleum contaminated soil. Another typical bioremediation process is to inject pollutant-degrading microorganisms into the contaminated environment, with or without at least one of an inducer which can induce expression of pollutant-degrading activity of the microorganism and a nutrient for supporting the growth of the pollutant-degrading microorganism. Compared to the conventional physical/chemical processes, such bioremediation processes can achieve remediation with low energy consumption and simple equipment. In addition, these processes can remedy the environment where the pollutant concentration is too low to be treated with physical/chemical processes.
In such a bioremediation process, it is necessary to inject a microorganism, an inducer, nutrients etc. into the environment, and how uniformly these substances can be injected into the contaminated environment is one of the requirements which decide the efficiency of a bioremediation process.
Several methods have been disclosed on injection of necessary materials into the environment. For example, U.S. Pat. No. 5,133,625 describes the method of controlling injection pressure using an extensible injection pipe while measuring the injection pressure, flow rate and temperature. This method aims to keep decomposing activity of microorganism optimum by controlling the concentration of the microorganism and nutrients by adjusting the injection pressure. U.S. Pat. No. 4,442,895 and U.S. Pat. No. 5,032,042 disclose the method where the soil is cracked by injecting a gas or a liquid from an injection well by applying pressure, and it says that oxygen and nutrients required for microbial purification can be supplied in this step.
As an intensive method for remedying a highly contaminated region in order to achieve an efficient microbial remediation within a short period, there are methods to define the range of injection of a microorganism and nutrients. For example, U.S. Pat. No. 5,111,883 discloses the method of injecting liquid chemicals into the soil at horizontally and vertically determined sites by setting the relative position of injection well and extraction well. This method aims to provide a process for injecting liquid agents into a limited area of the soil in a geometrical manner. It is considered as a very useful method when applied to microbial remediation of soil because it can define the area of the soil to be remedied.
In order to inject microorganism or substances for maintaining high decomposing activity of a microorganism into a limited area of soil, one of the methods is to form an impermeable layer as a barrier in the soil at a certain distance from the injection well. Conventionally known methods to form such an impermeable layer include laying plastic sheets or forming an asphalt layer in the soil, and injecting the soil with a treating agent such as cement, water-glass, urethane, acrylic amide, acrylate and so on. Japanese Patent Publications No. 2-26662 and No. 5-27676 disclose a method of forming an impermeable layer in a certain soil area using a water soluble polymer which turns water insoluble due to the ions in the soil. This method provides an impermeable layer as a barrier which limits the movement of substances and could be applicable to the process for injecting microorganism and nutrients into the limited area of the soil. An efficient and uniform injection of a liquid agent into a specific region has been attempted by using such region-defining means.